The present invention relates to a technique for jetting a very small amount of liquid as a droplet of specified volume to a plurality of areas from nozzle orifices.
An ink jet recording head capable of jetting a very small amount of liquid to a target position with relatively high accuracy is applied to a liquid jetting apparatus, such as a textile printing apparatus or a micro-dispenser.
In order to improve jetting efficiency, the number of nozzle orifices is increased. The amounts of liquid jetted from nozzle orifices by one operation are subjected to a maximum variation of ±10% approximately. In order to eliminate the variations, components constituting a recording head, such as nozzle orifices, a pressure generation chamber, and a pressure generator, must be manufactured with high accuracy, which in turn results in a significant upsurge in costs of a recording head to be used for an application of this type.
In order to prevent this problem, Japanese Patent No. 3,106,104 describes an ink jet head, in which a pressure generation chamber equipped with a heating element for generating thermal energy, as a droplet jetting member. In this patent, there is proposed formation of a drive signal by use of a pair of pulse signals; that is, a pre-heat pulse signal whose pulse width is adjustable, and a heat pulse signal whose pulse width is constant. The drive signal is supplied to the heating element. The temperature of liquid is adjusted by means of the pulse width of the pre-heat pulse signal, and a given volume of liquid is jetted in accordance with a heat pulse signal for jetting purpose. There is also described a method of rendering constant the pulse width of the pre-heat pulse signal and that of the heat pulse for jetting purpose, and of rendering variable the number of droplets to be jetted to a plurality of regions, thereby jetting liquid of uniform amount to the regions.
According to the related technique, the volume of liquid to be jetted can be controlled with practical precision by use of an ink jet head having specifications applied to a general-purpose apparatus. However, such a technique requires heating of liquid to its boiling point for jetting a droplet. Heating may degrade some types of liquid. Hence, limitations are imposed on the range of liquids to which the related technique is applicable. Further, the related technique requires the pre-heat pulse signal in addition to the heat pulse signal for jetting droplets, thereby complicating a control structure.